Nearshore habitat restoration through dam removal, Elwha River, Washington

Dams on the Elwha River have reduced sediment transport to the nearshore for almost a century. Following dam removal in 2009, increased supply of sediment to the Strait of Juan de Fuca may end, or perhaps reverse, the current trend of erosion along the river delta and may provide physical conditions and/or substrate for nearshore habitat change. Historic data document a general trend of erosion along the delta resulting in a net loss of ~65,000 sq. meters of land between 1926 and 1995. Oral histories also suggest a change of beach grain-size from sand-and-gravel to cobble, which coincided with losses of harvestable clams. Kelp beds, shellfish and eelgrass distributions may be key indicators of substrate-induced habitat changes in the nearshore following dam removal and are being monitored with our combined programs. Kelp beds have been observed offshore the delta, and no detectable change (p<0.01) in kelp species or canopy area has been observed during 1989-2005. Inventories of shellfish and substrate are made by underwater dives at three Elwha delta sites and a number of regional reference sites with annual frequency. Eelgrass beds along the Elwha delta were documented in 2006 during a multi-week underwater videographic survey. Variations in sediment size and beach profiles around the delta are being documented with a combination of physical samples, photography, videography, sonar, and topographic/bathymetric mapping. Continued monitoring of the nearshore substrate and habitats is planned through the multi-year dam removal process and should characterize the magnitude and nature of nearshore restoration.